Hadith 2:483

Narrated Abu Huraira:

When Allah's Apostle died and Abu Bakr became the caliph some Arabs
renegade (reverted to disbelief) (Abu Bakr decided to declare war
against them), 'Umar, said to Abu Bakr, "How can you fight with these
people although Allah's Apostle said, 'I have been ordered (by Allah)
to fight the people till they say: "None has the right to be
worshipped but Allah, and whoever said it then he will save his life
and property from me except on trespassing the law (rights and
conditions for which he will be punished justly), and his accounts
will be with Allah.' " Abu Bakr said, "By Allah! I will fight those
who differentiate between the prayer and the Zakat as Zakat is the
compulsory right to be taken from the property (according to Allah's
orders) By Allah! If they refuse to pay me even a she-kid which they
used to pay at the time of Allah's Apostle . I would fight with them
for withholding it" Then 'Umar said, "By Allah, it was nothing, but
Allah opened Abu Bakr's chest towards the decision (to fight) and I
came to know that his decision was right."